The traveling vortex system generated by an aircraft constitutes the principal ingredient to wake turbulence at airports. Typically, twin, counter-rotating vortices originate from the wings of the aircraft, near the wing tips. The rotational air flows are capable of upsetting, damaging, or causing loss of control to other aircraft. The problem is most acute in the airport environment, especially when successive planes are taking-off and landing on the same runway or adjacent runways.
Airport runway usage procedures have been established to minimize the threats to safety from wake turbulence. Minimum separations are used for aircraft on the same runway or runways, which are near to each other. The safety specifications limit the takeoff and/of landing rates.
The spacings required by these regulations are tied to the worst-case dissipation of the vortexes. The separation times are typically on the order of two minutes. This is related to the time it takes the vortices produced by an airplane to be substantially dissipated such that they will not harm a subsequent airplane on the runway, even if it is much lighter, and smaller, than the preceding plane.
These separation times, however, are maintained even though the vortices may have been blown clear of the runway by crosswinds, for example. The separation times must be maintained because there is no knowledge of vortex position.
Systems have been proposed that utilize ultrasound to detect wing-generated vortices. Ultrasonic-based systems have a number of advantages including a well understood core technology, and that existing ultrasonic transducers can be located on the airport runway and survive the associated environmental extremes of temperature and moisture.